Known nasal sprays generally produce droplet-sprays by mechanical means. The sprays so produced contain droplets within a broad range of droplet diameters which significantly reduces targeting accuracy and hence accuracy of dosing. The non-uniform nature of the sprays can also be very wasteful of medicament.
Dispensing devices are known which produce a finely divided spray of liquid droplets by electrostatic (more properly referred to as `electrohydrodynamic`) means. The droplet spray in such devices is generated by applying an electric field to a liquid at a spray head or spray edge. The potential of the electric field is sufficiently high to provide comminution of the liquid from the spray head. The droplets produced are electrically charged and thus are prevented from coagulating by mutual repulsion.
We have now discovered that electrohydrodynamic spray technology may be used to deliver charged monodisperse liquid droplets sprays, especially medicament sprays, to the upper respiratory tract and especially to the nasal mucosa, in an efficient and very controllable manner.
We have also discovered that for optimum targeting of the spray in the upper respiratory tract it is desirable to partially remove the electric charge from the droplet sprays produced by electrohydrodynamic comminution devices. To date the principal method used to effect charge removal has required the use of a discharging electrode having a sharp or pointed edge and located downstream from the spray head. This discharging electrode produces a cloud of charged ions from the surrounding air having an opposite electrical charge of equal magnitude to that on the comminuted liquid spray. In use, the ion cloud is attracted towards, collides with and thereby electrically discharges or partially discharges the liquid spray.
European Patent number 0234842 discloses an electrohydrodynamic inhaler wherein the spray of charged droplets is discharged by means of such a discharge electrode. The droplets are discharged in order to facilitate droplet deposition into the respiratory tract as otherwise the electrically charged droplets would deposit onto the mouth and throat of the user.
A particular problem associated with the use of the sharp discharge electrode is that the highly mobile ion cloud from the discharge electrode often interferes with the comminution of the liquid spray. The inhaler device of EP 0234842 attempts to ameliorate the effects of the ion cloud at the spray head by using a neutral shield electrode located close to the spray head. In addition, the level of control over the partial discharging of the liquid spray, especially the uniformity of charge across the spray cloud, tends to vary within wide limits between zero and the original maximum.